Implantable infusion devices are well known in the art and have been used to treat a variety of conditions or diseases such as pain, spasticity, and cancer. These infusion devices typically include a liquid medication reservoir within a housing or bulkhead. Some form of fluid flow control is also provided to control or regulate the flow of fluid medication from the reservoir to the outlet of the device for delivery of the medication to the desired location in a body, usually through a catheter.
Active drug infusion devices feature a pump or a metering system to deliver the drug into the system of a patient. An example of such a drug infusion pump currently available is the Medtronic SynchroMed programmable pump. Such devices typically include a drug reservoir, a fill port, a pump to pump out the drug from the reservoir, and a catheter port to transport the drug from the reservoir via the pump to a patient's anatomy. The drug reservoir, fill port, pump, and catheter port are generally held in a housing, or bulkhead.
The bulkhead typically has a series of passages extending from the drug reservoir and through the pump that lead to the catheter port, which is typically located on the side of the bulkhead. The drug is pumped through a catheter connected to the catheter port, and is delivered to a targeted patient site from a distal end of the catheter.
Often, a bacterial filter is present within the infusion device to filter the drug prior to being expressed into the patient. In some device designs, the filter is positioned between the reservoir and the pump.
Various types of implantable infusion devices are known. Two common classes of infusion devices are positive pressure (where the pressure in the reservoir is positive in relation to its surrounding volume in the bulkhead) and negative pressure (wherein the pressure in the reservoir is negative or neutral to its surrounding volume in the bulkhead). A positive pressure reservoir may be provided by a pressurizing means so that the contents of the reservoir are continuously pressurized. The pressurizing means may simply be a spring loaded actuator acting on a flexible bag type reservoir or may incorporate pressurized gas on flexible metal reservoir, or a resilient bag to constantly maintain the contents of the reservoir under pressure. Examples of positive pressure infusion devices are typified by U.S. Pat. No. 4,838,887 (Idriss), U.S. Pat. No. 5,049,141 (Olive) and U.S. Pat. No. 7,255,690 (Gray et al.). For a negative pressure or neutral device, the reservoir is not pressurized, but rather, the drive mechanism draws the fluid from the reservoir. In some devices, the drive mechanism uses electromagnetic and mechanical forces to move a piston between retracted and forward positions, thus drawing the fluid medication from the reservoir, through an inlet and forcing it out an outlet. An exemplary drive mechanism of this type is disclosed in U.S. Pat. No. 6,997,921 (Gray). With a negative or neutral pressure reservoir, the liquid must be drawn out of the reservoir and into the drive mechanism in order to prime the drive mechanism. This requires that the drive mechanism include features for drawing the fluid medication from the reservoir and through a flow path to the outlet chamber rather than receiving the fluid medication via positive pressure. Examples of negative pressure infusion devices are typified by U.S. Pat. No. 4,482,346 (Reinicke) and U.S. Pat. No. 4,486,190 (Reinicke).